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from bisect import bisect_left
from itertools import accumulate
a = [2, 2, 0, 4, 2]
k = 2
a = [0] + a
n = len(a)
ans = 0
pf = list(accumulate(a))
locations = defaultdict(list)
for j in range(n):
locations[pf[j] - j * k].append(j)
for i in range(n):
ans += bisect_left(locations[pf[i] - i * k], i)
print(ans)